1. Field of the Invention
The present invention relates to the chip thickness in the layered direction of a compound semiconductor light emitting element chip and the reflectance at the top plane and bottom plane of the chip, wherein the compound semiconductor light emitting element is layered on a translucent substrate. The present invention particularly relates to a light emitting element from which high light output is obtained.
2. Description of the Background Art
FIG. 6 is a schematic sectional view of a chip of a conventional light emitting element structure. On a translucent substrate 100, an N type nitride compound semiconductor layer 200, a P type nitride compound semiconductor layer 300, a P type translucent electrode 400, a P type pad electrode 500 and an N type pad electrode 600 are arranged. The translucent substrate 100 side is placed at the cup bottom of a lead frame using paste. In FIG. 6, d denotes the chip thickness of the translucent substrate 100 and the layered body stacked thereon. The arrow in the chip represents the guided wave of light generated inside the chip. Regarding the chip thickness, Japanese Patent Laying-Open No. 5-343742, for example, discloses the adjustment of the thickness of a sapphire substrate to 50 to 300 μm in a chip fabrication method.
In the above conventional light emitting element, the light generated at the light emitting layer within the chip is emitted outside through P type translucent electrode 400 located at the top of the layered body for usage. Therefore, P type translucent electrode 400 must have transmittance with respect to the generated light. However, P type translucent electrode 400 is formed of a thin metal film. Therefore, the transmittance at P type translucent electrode 400 is only approximately 50% to 70% (30% to 50% in reflectance). The light generated at the light emitting layer is partially lost when emitted outside of the light emitting element. The light output from the element is weak. Only light of low intensity could be obtained. The light emitted from the light emitting layer is also issued downwards (here, towards the substrate) and laterally in addition to the upwards direction, i.e., towards P type translucent electrode 400. As indicated by the arrow in FIG. 6, some of the light emitted from the light emitting layer advances downwards to be reflected at the bottom of the substrate, and then partially reflected again at the top P type translucent electrode 400 to advance downwards again towards the substrate. Thus, light travels in a repetitious manner thereof. This means that the light to be emitted outwards will be blocked by P type translucent electrode 400 (reflectance R1) or P type pad electrode 500. Also, the light reflected at the backside of the substrate (reflectance R3) to advance upwards is also blocked by N type pad electrode 600 (reflectance R2). Thus, multiple reflection of the generated light occurs at the top plane of the conventional light emitting element where the electrode is formed and at the backside of the substrate, so that light will not be easily output from the light emitting element. There is also the problem that the light is absorbed at the P type electrode or N type electrode to result in reduction of the light output. The light emitting element of the conventional structure had the disadvantage that the output of the entire light generated from the light emitting layer is reduced.